A blog about building a DIY CNC laser cutter / engraver from mostly recycled parts.

Tuesday, December 21, 2010

Gutting printers for steppers

Immediately after I started drooling at the DIY CNC videos on the 'net, I found two printers in the garbage. What luck! There's the free stepper motors I was hoping for! Or so I thought.

The models were HP Deskjet 5150 and Deskjet 656C.

HP Deskjet 656C straight outta garbage.

After all the trouble of carrying them home, I noticed they both had plastic optical guides next to the printhead pulley system. At first I was thinking "why do they need optics to guide steppers?" Then I understood the grave situation. There were no steppers. It seems that HP has found a cheaper way to get their precise printhead movement. They use DC motors with optical linear encoders to give feedback on the printhead's position.

HP's optical guide for the printhead.

I decided anyway I would gut the both printers for parts. I would probably be needing them for the mechanical construction.

You need a torx screwdriver set to open these things. Every screw on these seems to be a torx. I needed at least the T10, T15 and T20 to open the printers.

My trusty screwdriver set.

At this point I want to make it clear that opening printers is MESSY! Be prepared to get ink everywhere.

A partially gutted HP Deskjet 5150.

I found another optical guide on the Deskjet 5150. It's a rotary encoder that gives the printer feedback on the paper feed DC motor's position. Again they have saved on steppers.

An optical rotary encoder.

And then I found my first stepper! On the Deskjet 656C they still use a proper stepper for the paper feed motor. I need one more for the build.

Even without google it's easy to distinguish a stepper motor from a DC motor. Stepper motors have 3-6 wires on them while DC motors have only 2. For more info on the various motor types, here's a great tutorial page: Jones on Stepping Motor Types.

So here's the conclusion: if you're looking for steppers: Deskjet 5150's got zero, 656C has one.

But the Deskjet 5150 sported something else I'm sure I'll find useful: a screw-mountable metal rod that the laser head can travel on.

I'm planning to use this rod in the CNC build since it's got some convenient screw holes.